XYZ feed rate on 3d cut

LowRider CNC Troubleshooting
21

BTW, F3000 is 50mm/s in the firmware, and F480 is actually 8mm/s. The F numbers are mm/min. Just to make that clear.

So let me expand on Ryan’s example. Let’s say you have a move which is 10mm in X and 1mm in Z. The move is along the triangle, not 10mm in X and then 1mm in Z. If your max speed in Marlin for Z is 1mm/s and your max speed in X is 10mm/s, then Marlin can make this move in 1 second. It will be going 10mm/s in X and 1mm/s in Z, and a total of 10.05mm/s.

If you are moving only in X, then the Z speed won’t limit you at all. Your XY moves are going to be done at F3000.

If you are moving only in Z, then the speed will be limited to the rate in the firmware, which is 8mm/s.

In the example above, if the feedrate for that move in gcode was set to F300, or 5mm/s, then the speed along the diagonal would be limited to 5mm/s, and it would be underneath the top speed of either the X or the Z.

So if your X,Y max feedrate in the code is set to 40, and your F is 3000 in the gcode, but your Z in Marlin is set to 8mm/s, then a move like above, with 10 in X and 1 in Z would not be limited by the Z at all. You’d have to go 80mm/s in X before the Z component would slow you down.

Let me make a longer example.

Imagine you could only go 30 mph in the north direction. No matter what else happened, if you went north by 30 miles in less than one hour, you would get a ticket.

Imagine you had the same restriction to only go 40mph in the east direction.

If the road you were on was going straight north and if the speed limit on that road was 20mph, then you could only go 20mph. If it was 90mph, you could only go 30mph (That’s as fast as you can go north).

If the road you were on was going straight east, and the speed limit on the road was 90mph, you could only go 40mph.

If you had a road that was north-east though, at the correct angle, you could go 30mph north while going 40mph east. That would mean you were going 50mph along the road.

Is this making sense? Marlin is going to make sure that you don’t exceed the Z speed in the Z direction. It’s going to make sure you don’t exceed the X speed in the X direction, and it’s going to make sure you don’t exceed your feedrate along the direction you’re actually going.

You can fix it with CAM, but there are shapes that can’t be fixed that way, and I think changing the Z speed in the firmware would solve a lot of headaches.

3 Likes
22

So I have it set to parallel to X. If it is parallel to y, it would constantly be changing z, and it takes much longer like you mentioned. It does make the z movements at the end of the row, they are just too fast for the machine to handle and it skips. Each x pass should not really need a z movement during the pass, it’s fine for it make the entire z movement before starting the x pass. That’s why I mentioned just making the x pass, move the step over amount in y and make another pass in the opposite x direction. Continue that pattern dropping the z to the desired height at the end of each x pass. I actually need it to operate like a 2d cut, but instead of a single depth, I need it to follow the contour. If the only way to do this is to modify the gcode, that’s what I will do. I can’t run the z at high speed, and I can’t run the x or y at low speed.

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What board, step rate, and lead screw do you have, what are your rapids and plunges for Z set at?

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In firmware z was set to 30, I changed it to 8. What I really need from the machine is for a line of code to be:

G01 x203.000 z-10.8765 F3000

and have it move along x at 3000, and z at a speed that doesn’t cause the motors to skip. When I ran it with the F(xy) set to 3000, at the end of each x pass, it skipped. This is very much like linear pocketing, but with a variable depth along the contour, instead of just a final depth.

So hopefully changing the limit in firmware will do the trick. Really that should be set to a number that won’t allow the motors to skip anyway, as I will change the speeds for different bits and materials often, but the machine can only go up so fast and that will not change.

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Rambo 1.4, not sure on step rate, lead screws from you, rapids are 2100 and 480 like the guide shows, and plunge rate in Estlcam was 180, at 39 mm depth. Again, foam is the material I am cutting, not just testing with.

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This is what I am making. It really shouldnt need to change z while moving in either x or y. Just change z before moving on the next x pass.

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As we both tried to explain it does not work that way. Also the firmware limit is not always followed. I has to be set properly in CAM.

f3000=50mm/s Way too fast.

 

Why don’t you post a screenshot of your settings screen for this cut as that is not the right information.

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This is exactly what the firmware setting should do. It shouls keep you from losing Z steps in other situations too.

Can you do a fast test? Just the trouble area?

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Also depends on which version of Marlin you are using. The newer versions of Marlin incorporate a better limiting on feedrates.

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Jeff - I am not home currently, and wont be until later (kids thing at school), but I will try with the setting lower and see what happens.

Ryan - The gcode has F3000, but there is no way its traveling 50mm/s. The piece is 203mm in the x direction, and it takes about 22 seconds to cross that, so only about 9mm/s. Probably the z limit slowing it down as you said. I just kept bumping F(xy) trying to get the time down. Foam shouldnt put up that much of a fight.

BT - I’m using 2.0 that just came out

Really the issue here is that it is doing the entire Z movement at the end of the row is really fast, and when it gets to the part of the contour where it starts going back up, it loses Z on one side. I just want to limit Z going up, without limiting X and Y.

Sorry if this posts more than once, it isnt showing up after I post it.

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31

When I watch the preview, I am pretty sure I can see where it skips. It made a big jump when I was testing it yesterday. It does not appear to make any Z movement along the X pass, if it did, it wouldnt be a flat pass, it would slope along X. Ryan you keep saying it doesnt work that way, but why couldnt it for this specific case? Following the formula: cut along X, move forward Y, drop Z (if needed), cut along X the other direction, move forward Y, drop Z (or up for that matter), cut X, etc… I think this should work. That is basically what it is doing anyway, its just too fast for the Z. (and likely XY too since its probably not moving at F3000 anyway). If I split the Z movements from the X, and drop it to a new line, I can change the F rate to something Z can handle. It would be tedious, but I dont see why it wouldnt work.

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Your gcode and pictures of your settings?

I think all of us are talking about different things.

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The gcode will have to wait a bit, till I get home. The settings are two posts back.

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What material is this in?

Your version of this page?

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Cutting the pink XPS foam board. I don’t have my laptop with me, but that page looks just like mine.

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Firmware or the previous setting are wrong.

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You 100% sure that previous page does not say mm/s?

What board drivers and version of firmware then?

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Latest FW, from December. 2.0 I believe. I will grab screen shots when I get home.

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There will be a number so we know exactly what version. My hardware and board, all of it?

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Yes everything from you, but I updated FW. I also updated to Estlcam 11.